This project analyses the impact in the mechanical properties of Polyoxymethylene (POM) of three different blends of biodiesels: B0 with 0% of Rapeseed Methyl-ester (RME), B20 with 20% of RME and B100 with 100% of RME. Polyoxymethylene specimens have been subjected to an accelerated aging during 1600 hours at 85ºC. This is the equivalent to 20 years of life time. In addition, a thermal oxidation in air at the same temperature has been performed to check the impact of the temperature in the final degradation.Three different methods have been performed to calculate the diffusion rate, however and one of them has been selected for its reliable results. The second Fick´s law have been chosen to model the diffusion. The diffusion rate has been calculated for the B20 and B100 blend due to the B0 blend has a non-constant diffusion rate. B20 shows also some divergence while B100 fits the Fickian behaviour.A Finite Different approximation method has been used to predict the concentration profiles of the diffusion process of B20 blend. They have been compared with the results of the IR Microscope, with a clear misalignment between the expected and the actual values.Tensile tests have been done in different stages of the test to check the stress-strain behaviour of the specimens for each aging type. The most relevant parameter of degradation is the Elongation At Break (EAB), which decrease considerably a cause of the embrittlement. A study of the real stress-strain has been also done to assure the real behaviour of the material.A fracture surface study through Scanning Electron Microscope (SEM) and Light Microscope has been done to assure the brittle behaviour with the aging and the changes in the structure of the material.The swelling behaviour has been also modelled, and the bases for a future FEM analysis have been exposed.

No description available.

Rapid compensatory reach-to-grasp reactions are prevalent and functionally important responses to instability. The need to react very rapidly (to prevent falling) imposes temporal constraints on acquisition and processing of the visuospatial information (VSI) needed to guide the reaching movement. Previous results suggested that the CNS may deal with these constraints by using VSI stored in memory proactively, prior to perturbation-onset; however, the extent to which online visual control is necessary or sufficient to guide these reactions has not been established. Furthermore, the influence of memory-decay and concurrent cognitive-task on the performance of these reactions has not been examined. This Thesis employed a novel paradigm wherein the participant is stationary and a motor-driven handhold is positioned unpredictably in front of the participant for each trial. Reach-to-grasp reactions were evoked in healthy young and older adults by sudden unpredictable antero-posterior platform translation (barriers deterred stepping reactions). Liquid-crystal goggles were used to occlude vision either before (recall-delay time=0s/2s/5s/10s) or after perturbation-onset to force reliance on either stored- or online-VSI, respectively. Participants performed a spatial- or non-spatial-memory task during the delay-time in a subset of trials. When forced to rely on stored-VSI, all participants showed reduction in reach accuracy; however, a tendency to undershoot the handhold was exacerbated in the older adults. Forced-reliance on online-VSI led to similar delays in all participants; however, the older adults were more likely to reach with the “wrong” arm or raise both arms. Comparison with normal-VSI trials suggests that both sources of VSI are utilized when grasping the movable handhold for support, with stored-VSI predominating during initiation/transport and online-VSI contributing primarily to final target acquisition/prehension. In terms of recall-delay, both age groups showed comparable reduction in medio-lateral endpoint accuracy when delay-time was longest. Moreover, both cognitive tasks had similar (slowing) effects in both age-groups, suggesting these effects were related to generic attentional demands. However, the older-adults also showed a dual-task interference effect (poorer cognitive-task performance) that was specific to the spatial-memory-task. Further research is needed to establish whether interventions aimed to improve visual/cognitive processing speed, visuospatial memory, and/or attention capacity can reduce risk of falling among senior populations.

This research examines age differences in the use and value of memory compensation strategies for everyday memory tasks. Chapter 1 reviews the literature on memory compensation and aging. According to Selective Optimization with Compensation (SOC) model, older adults may be more likely than younger adults to take advantage of memory compensation strategies when they are available. Chapter 2 describes a diary study in which older and younger participants rated the extent to which they use compensation strategies in everyday life and reported everyday memory errors over the course of a week. Older adults reported fewer memory errors than younger adults and more use of memory aids. However, use of memory aids was unrelated to frequency of memory errors in either age group. Chapter 3 reports a laboratory experiment on the use of memory aids for recalling phone messages. Participants listened to phone messages while simultaneously completing a seating chart, and were asked to report the content of the messages to the experimenter. Participants were either allowed to use a memory aid for the phone message task, or not. Older participants reported using compensation strategies more frequently in everyday life, but they were no more likely than younger participants to search for or employ an aid in the phone message task. Using a memory aid was differentially beneficial, improving performance more for older than younger participants. In Chapter 4, participants completed two phone message recall and two seating plan tasks. Participants were encouraged to use whatever in the room that they might find helpful. On one round of tasks a pen was tied to a clipboard and participants could use it to write down the phone messages. On the other round no pen was available. The order of the trials was counterbalanced across participants. This design examined the calibration between participants’ use of memory aids and their performance on the recall task – whether participants’ performance on the first trial predicted their subsequent use of memory aids, and whether participants who chose to use a memory aid when it was available on the first trial performed particularly poorly on the second trial when no aid was present. As in Study 1, older adults reported using memory aids more frequently in everyday life but age was unassociated with whether or not participants used the pen when one was available. There was little evidence of calibration. Participants’ memory performance on an initial trial had little impact on their use of a memory aid on a subsequent trial. Participants who used a memory aid on the first trial actually recalled more phone message details on the second trial (without the aid) than those who did not. This was true for both age groups. Chapter 5 reflects on older and younger adults self-reported and observed uses of memory compensation strategies. Across all 3 studies older adults reported using external memory aids more frequently in everyday life. However, contrary to the SOC model, in Studies 2 and 3 there were no age differences in older and younger adults’ use of a pen to write down phone messages on the lab task. Nor was participants’ choice to use the memory aid associated with their unaided performance on the task. These results do not support the prediction derived from SOC that older adults use compensation strategies more frequently or more sensitively than younger adults. However, using the memory did improve performance on the task more for older than for younger adults. These results support the hypothesis that external memory aids are a particularly valuable strategy for older adults and suggest the need to better understand why some individuals engage in compensation use and others do not.

Lower body negative pressure (LBNP) is frequently used in the research setting as a means to induce orthostatic stress. This tool is applicable to typical movements during daily living only if the associated responses are comparable to those of actual posture change. The purpose of this project was to investigate the correspondence between these two conditions in a group of elders with mean age of 74 ± 2 years. The primary hypothesis predicted very similar physiologic responses between LBNP and posture change. During LBNP, orthostatic stress was sufficient to reduce stroke volume (SV; p=0.0097), which was related to splanchnic pooling (r=-0.833; p=0.0020). Diastolic cerebral blood flow velocity (CBFV) was directly related to central venous pressure (r=0.683; p=0.0360), strengthening the notion that an important determinant of CBFV during LBNP is incoming pulsatile flow into the cerebral circulation. This is in contrast to what occurred during posture change (p=0.0355), where diastolic CBFV decreased significantly (p=0.0288) and was directly related to diastolic blood pressure (DBP; p=0.0427), highlighting the role of cerebral perfusion pressure (CPP) in maintenance of CBFV particularly during upright posture. In both conditions, DBP was related to cardiac output (Q) and total peripheral resistance (TPR). The relative heart rate (HR) response was higher during posture change than during LBNP (p=0.0397), suggesting that a negative pressure of up to 40 mmHg may not be adequate to elicit the same HR responses as true orthostasis in this elderly population. Contrary to the initial hypothesis, the HR and diastolic CBFV responses were different between the two conditions. Importantly, the results of this study support that in response to both actual orthostasis and simulated orthostasis, elderly persons experienced a drop in CBFV, but for different fundamental reasons, which were directly attributable to distinctions in the effects of gravity during the two postures. Recognizing the mechanistic differences in cerebro- and cardiovascular responses between true and simulated orthostasis is essential, and in this elderly population, there were important differences to consider.

No description available.

Mitochondrial dysfunction is considered as a key mechanism of aging but little is known about the impact of mitochondrial biogenesis. Mitochondrial DNA (mtDNA) copy number control is an important aspect of mitochondrial biogenesis and is highly regulated in eukaryotic organisms. By studying mtDNA copy number, our aim is to gain a better understanding of the relationship between mitochondrial biogenesis and aging. We developed an optimized protocol for measuring mtDNA copy number in Caenorhabditis elegans using quantitative real-time PCR (qPCR). We investigated how mtDNA regulation is affected by a variety of aging-related pathways. We found the insulin/IGF-1 signaling (IIS) pathway regulates mtDNA content in a DAF-16- and UCP-4-dependent manner. By utilizing RNA interference (RNAi) against polg-1, we showed that mitochondrial stress likely modulates lifespan through the IIS pathway. Our work identifies IIS as a communications pathway between mitochondria and the nucleus in modulating mitochondrial biogenesis and lifespan in Caenorhabditis elegans.

Diss. (sammanfattning) Umeå : Univ., 2003. / Härtill 4 uppsatser.

Dissertation (Ph.D.).--University of Texas Graduate School of Biomedical Sciences at San Antonio, 2006. / Vita. Includes bibliographical references.

Thesis (Ed. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 260-269). Also available via the Internet